In the Hidaka Coastal Area, the Earthquake off Urakawa, March 21, 1982 (Magnitude 7.1) caused crustal deformation in the form of vertical displacement and land-surface change such as fissure, landslide, cliff collapse, etc. The characteristics of crustal deformation can be inferred from damage ratio, location of surface breaks, elevation change and aftershock distribution.
Regional differences of damage ratio were recognizable in the stricken area. The damage ratio is high in the area in which the representative structural trend is parallel to the strike of main hypocentral fault plane. The damage ratio is low in the area in which the struc-tural trend crosses the strike of main hypocentral fault plane. Thus regional differences of damage ratio seem to be controlled by geological structure.
In the Niikappu and Higashi-Shizunai areas, surface breaks and accompanying damage to artificial structures occurred along pre-existing fault lines. This suggests that surface faults in both areas were caused by re-movement at the present earthquake. The re-move-mentof Seppu Fault in Niikappu which is located far from the hypocentral region seems to be induced by intense shocks of earthquake as was the case with the past two earthquakes (occurred off Tokachi in 1952 and 1968). In contrast, the movements of Harutachi Anticlinal Fault and a northern paralleling fault in the Higashi-Shizunai area can be assumed to be earthquake faults.
Data of re-levelling show that the Higashi-Shizunai area is corresponds to the center of conspicuous regional uplift. From aftershock distribution, the conspicuous uplift seems to be caused by a secondarily hypocentral faulting which occurred shallower than the main faulting. This suggests that the surface fault movements in the Higashi-Shizunai area resulted from the secondarily hypocentral faulting.

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At the northwestern foot of the Daisen volcano, which has a relative height of about 1, 700m above the foot, many alluvial fans different in age widely develop. The surfaces are divided into six groups according to their ages; Older fan I (OF I), Olderr fan II (OF II), Middle fan (MF), Younger fan I (YF I), Younger fan II (YF II) and Youngest fan (YTF). The ages were estimated from the stratigraphic relations of the fan deposits to marker tephras.
The MF, YF I and YF II fans are developed downstream of the valleys, in which the Nawa pyroclastic flow deposits (Nw), the Makibara pyroclastic flow deposits (Mk) and the Odori pyroclastic flow deposits (Od) are distributed, respectively. The fan deposits are composed of the materials supplied from the related pyroclastic flow deposits.
The process of MF, YF I and YF II fan formation is summarized as follows:
1. A pyroclastic flow containing many rock fragments of cobble to boulder size was deposited on the bottom of a radial valley dissecting the body of the volcano.
2. When the pyroclastic flow deposit was loose, or not welded, the river immediately started to erode it.
3. The gravel and sand were transported from the downstream tip of the pyroclastic flow deposits mainly in the form of debris flow.
4. The debris flows formed alluvial fans at the foot of the volcano, where the slope becomes gentle and wide plains develop.
The ages of the fan surfaces of MF, YF I and YF II are 90, 000_??_100, 000 y. B. P., ca. 20, 000 y. B. P. and 7, 000_??_10, 000 y. B. P., respectively. The ages of the pyroclastic flow deposits of Nw, Mk and Od are ca. 100, 000 y. B. P., 25, 000_??_30, 000 y. B. P. and ca. 17, 000 y. B. P., respectively. Therefore, the time needed for the fan formation is estimated as less than 5±10³ or 1±10⁴ years. This indicates that the period of fan formation at the foot of volcano is very short as compared with the life of a large volcano, which is in the order of 10⁵ years.

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